A conventional seat lifter used for a seat of a vehicle is disclosed in the Japanese Laid-Open Utility Model Nos. 60-16622 and 60-90030, for example, in which the front and rear sides of the seat are independently lifted up.
In these seat lifters, a balance spring is disposed between one side frame and a connecting shaft on the rear end side, and between the other side frame and a connecting shaft on the front end side so as to smoothly perform lifting operations in front and rear end portions of the seat frame.
One end of each of the balance springs is engaged with a projected hook disposed in the connecting shaft on the front and rear end sides of the seat frame, and the other end of each of the balance springs is engaged with a projected hook disposed in the right and left side frames.
Accordingly, the balance springs are individually disposed with respect to front and rear end lifts in the independent seat lifters on the front and rear sides of the seat. Thus, the space for disposing the balance springs therein must be fairly large, the mechanism thereof is complicated, the number of parts is large, and the weight is also heavy, thereby increasing the manufacturing cost of the seat.
The seat lifter is an apparatus for raising and lowering a seat cushion within a certain height range from the floor of the vehicle, and is constituted to secure an optimum driving position for the driver. The seat lifter of this kind is composed of a first type in which front and rear portions of the seat cushion are independently adjusted to be raised or lowered, and a second type in which only the front portion of the seat cushion can be raised or lowered. In the first type, a pair of operating portions for adjusting the raising and lowering operations of the seat cushion are disposed to individually operate the front and rear portions of the seat cushion.
In the conventional seat lifter of the first type, a lower frame is directly fixed to a chassis, or is fixed to the chassis through a slide rail. An upper frame for fixing the seat cushion thereto is disposed above the lower frame such that the upper frame can be raised or lowered through right and left links on the front and rear sides thereof. Sector gears for raising the links are respectively fixed by welding to connecting shafts for connecting the right and left links to each other, and can be rotated through pinions of a pair of spring brake devices rotatably supported by the upper frame. Each of the spring brake devices has a knob for rotating the device at one end thereof and adjusting the raising and lowering operations of the seat, and a pinion engaged with each sector gear at the other end of the device so that each spring brake device is rotatably supported by the upper frame. In addition, each spring brake device has a brake unit between the pinion and the knob. Accordingly, when the knob is rotated, the pinion and the sector gear are rotated so that the link connected to the sector gear is raised and the other link is thereby moved in association therewith through the connecting shaft. Thus, the front or rear portion of the upper frame can be raised or lowered within a constant range, and the upper frame can be fixed in a desired setting position
However, in the conventional seat lifter mentioned above, the upper and lower frames are respectively composed of right and left side frames, and are overlapped through links in both right and left side portions forming a rectangle. The right and left links are respectively connected to connecting shafts on the front and rear sides of the upper and lower frames. A stereo-frame structure is thus formed, and is delivered as a completed product to a purchaser from a manufacturer. At the present time, the volume of a number of seat lifters is large, and the transporting cost thereof is thereby increased. The so called knock-down system is used in which the seat lifter is disassembled and delivered to the purchaser, and is then reassembled by the purchaser when the seat lifter is attached within a vehicle. However, in the conventional seat lifter, the connecting shafts and the sector gears are fixed by welding them to each other, and are thus integrally formed, so that they cannot be disassembled and assembled thereafter, or the assembling operation is greatly complicated since these members are not constructed to be disassembled and assembled thereafter.
Accordingly, the conventional seat lifter is not appropriately designed to be transported in a disassembled state so that it is necessary to improve the seat lifter for the knock-down system. Namely, the seat lifter must be constructed such that it is not necessary for the purchaser to perform welding operations and new working operations of the seat lifter, and such that the seat lifter is easily assembled.